Vladislav V. Lobodin

Cyclization of ortho-cyclopropylphenyl benzamides in gas and liquid phases.

The electron ionization (EI) and collision-induced dissociation (CID) spectra of substituted N-(ortho-cyclopropylphenyl)benzamides 1–7 and N-[ortho-(1-methylcyclopropyl)phenyl]benzamides 8–12 were recorded. In addition to routine bond cleavages, the molecular ions (M+) of 1–12 undergo cyclization into the corresponding 3-aryl-1-alkyl-1-ethyl-1H-benzoxazines and isomeric 5-ethyl-2-oxodibenzoazepines. The presence of a methyl group in the cyclopropyl ring (compounds 8–12) makes the formation of 5-ethyl-2-oxodibenzoazepine less favorable. In accord with mass spectrometric predictions, compound 13 (3-p-tolyl-1-ethyl-1H-benzoxazine) was obtained as a major product of the reaction of N-(ortho-cyclopropylphenyl)-4-methylbenzamide 1 with sulfuric acid. Traces of 5-ethyl-2-oxodibenzoazepine were also detected in gas chromatography-mass spectrometry (GC-MS) analysis of the reaction mixture although the yield was too low to allow its isolation.

Tetramethylammonium hydroxide as a reagent for complex mixture analysis by negative ion electrospray ionization mass spectrometry.

Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) enables the direct characterization of complex mixtures without prior fractionation. High mass resolution can distinguish peaks separated by as little as 1.1 mDa), and high mass accuracy enables assignment of elemental compositions in mixtures that contain tens of thousands of individual components (crude oil). Negative electrospray ionization (ESI) is particularly useful for the speciation of the most acidic petroleum components that are implicated in oil production and processing problems. Here, we replace conventional ammonium hydroxide by tetramethylammonium hydroxide (TMAH, a much stronger base, with higher solubility in toluene) to more uniformly deprotonate acidic components of complex mixtures by negative ESI FTICR MS. The detailed compositional analysis of four crude oils (light to heavy, from different geographical locations) reveals that TMAH reagent accesses 1.5-6 times as many elemental compositions, spanning a much wider range of chemical classes than does NH4OH. For example, TMAH reagent produces abundant negative electrosprayed ions from less acidic and neutral species that are in low abundance or absent with NH4OH reagent. More importantly, the increased compositional coverage of TMAH-modified solvent systems maintains, or even surpasses, the compositional information for the most acidic species. The method is not limited to petroleum-derived materials and could be applied to the analysis of dissolved organic matter, coal, lipids, and other naturally occurring compositionally complex organic mixtures.

Gas Chromatography/Atmospheric Pressure Chemical Ionization Tandem Mass Spectrometry for Fingerprinting the Macondo Oil Spill

We report the first application of a new mass spectrometry technique (gas chromatography combined to atmospheric pressure chemical ionization tandem mass spectrometry, GC/APCI-MS/MS) for fingerprinting a crude oil and environmental samples from the largest accidental marine oil spill in history (the Macondo oil spill, the Gulf of Mexico, 2010). The fingerprinting of the oil spill is based on a trace analysis of petroleum biomarkers (steranes, diasteranes, and pentacyclic triterpanes) naturally occurring in crude oil. GC/APCI enables soft ionization of petroleum compounds that form abundant molecular ions without (or little) fragmentation. The ability to operate the instrument simultaneously in several tandem mass spectrometry (MS/MS) modes (e.g., full scan, product ion scan, reaction monitoring) significantly improves structural information content and sensitivity of analysis. For fingerprinting the oil spill, we constructed diagrams and conducted correlation studies that measure the similarity between environmental samples and enable us to differentiate the Macondo oil spill from other sources.

Linking Natural Oil Seeps from the Gulf of Mexico to Their Origin by Use of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

We report chemical characterization of natural oil seeps from the Gulf of Mexico by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and Gas Chromatography/Atmospheric Pressure Chemical Ionization Mass Spectrometry (GC/APCI-MS), to highlight how FT-ICR MS can also be employed as a means to determine petroleum connectivity, in addition to traditional GC/MS techniques. The source of petroleum is the Green Canyon (GC) 600 lease block in the Gulf of Mexico. Within GC600, two natural oil seepage zones, Mega Plume and Birthday Candles, continuously release hydrocarbons and develop persistent oil slicks at the sea surface above them. We chemically trace the petroleum from the surface oil slicks to the Mega Plume seep itself, and further to a petroleum reservoir 5 km away in lease block GC645 (Holstein Reservoir). We establish the connectivity between oil samples and confirm a common geological origin for the oil slicks, oil seep, and reservoir oil. The ratios of seven common petroleum biomarkers detected by GC/APCI-MS display clear similarity between the GC600 and GC645 samples, as well as a distinct difference from another reservoir oil collected ∼300 km away (Macondo crude oil from MC252 lease block). FT-ICR MS and principal component analysis (PCA) demonstrate further similarities between the GC600 and GC645 samples that distinctly differ from MC252. A common geographical origin is postulated for the GC600/GC645 samples, with petroleum migrating from the GC645 reservoir to the oil seeps found in GC600 and up through the water column to the sea surface as an oil slick.

Cyclization of N,N-dialkylditiocarbamate and alkylxanthate derivatives of polyhalogenated pyridines in gas and liquid phases.

The intramolecular cyclization of 31 polyhalogen-substituted pyridines containing N,N-dialkyldithiocarbamate or alkylxanthate groups has been compared as a reaction in solution with sodium N,N-dialkyldithiocarbamates or potassium carbethoxydithiolate and as a gas-phase reaction under electron ionization (EI) conditions. A scheme of fragmentation for the studied compounds has been proposed. The influence of the nature of leaving groups (Cl, F, CF3, CN, COOEt), of the presence of electron-withdrawing groups (Cl, F, CN, CCl3, CF3, COOEt) that are ortho, meta or para to the leaving halogen, of the position of a dithio group with respect to the pyridine nitrogen atom and of the role of oxygen and nitrogen in the corresponding alkylxanthates and N,N-dialkyldithiocarbamates on the cyclization process has been investigated.

Charge Reversal Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

We report the first charge reversal experiments performed by tandem-in-time rather than tandem-in-space MS/MS. Precursor odd-electron anions from fullerene C60, and even-electron ions from 2,7-di-tert-butylfluorene-9-carboxylic acid and 3,3′-bicarbazole were converted into positive product ions (–CR+) inside the magnet of a Fourier transform ion cyclotron resonance mass spectrometer. Charge reversal was activated by irradiating precursor ions with high energy electrons or UV photons: the first reported use of those activation methods for charge reversal. We suggest that high energy electrons achieve charge reversal in one step as double electron transfer, whereas UV-activated –CR+ takes place stepwise through two single electron transfers and formally corresponds to a neutralization-reionization (–NR+) experiment.